Microbe-catalyzed processes are particularly useful in the production of a variety of chemicals known as fine or specialty chemicals.
Perhaps the most important commercial use of microbe-catalyzed processes is in the food industry. Exemplary of such processes is the production of high fructose corn syrup (HFCS) catalyzed by immobilized glucose isomerase. This process converts glucose to an approximately equimolar mixture of fructose and glucose; this mixture is referred to as HFCS.
Examples of other chemicals prepared by microbe-catalyzed processes are the L-amino acids, which are useful as food additives, in animal feed, and in medicinals. Though chemical synthesis may be simpler than fermentations at times to prepare amino acids, the chemical process almost always yields a racemic mixture of amino acids. This racemic mixture then has to be resolved to give the biologically-active L-amino acid. On the other hand, a microbe-catalyzed process will yield the L-amino acid predominantly.
Immobilization of an enzyme which catalyzes a microbe-catalyzed process generally gives better yields of desired product and preserves enzyme integrity. With regard to extracellular enzymes, immobilization is the physical or chemical containment of the enzyme so that the enzyme can conveniently be separated from the product and reused. Stabilization of enzymes by chemical stabilizers also preserves enzyme integrity. The immobilization or stabilization of the enzyme can be done while the enzyme is still in the living microbe (intracellular), or when the enzyme is in the cell-free state. The immobilization or stabilization techniques will vary in accord with these two enzyme states. Thus, it should be appreciated that immobilization or stabilization conditions effective for intracellular enzymes will not necessarily be appropriate for extracellular enzymes, and vice versa.
Prior art relating to the immobilization or stabilization of extracellular enzymes can be exemplified by the following U.S. patents:
U.S. Pat. No. 3,915,797--Enzyme bonded to a substantially water-insoluble anion exchange resin.
U.S. Pat. No. 3,982,997--Glucose isomerase adsorbed to the internal surfaces of a high surface area porous inorganic support material.
U.S. Pat. No. 4,077,842--A stabilized glucose isomerase concentrate is prepared by contacting an aqueous mixture containing cell-free glucose isomerase and a water-miscible organic solvent with a substantially water soluble magnesium salt.
U.S. Pat. No. 4,144,127--Glucose isomerase is immobilized by adsorption onto a colloidal silica.
U.S. Pat. No. 4,411,996--Glucose isomerase is stabilized by intramolecular crosslinking and copolymerization into a polymer matrix.